<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .red{color: red}
        .big{font-size: 30px;font-weight: bold}
        .small{font-size: 3px}
    </style>
</head>
<body>
    <div id="app">
       <span class="red" v-class="msg">
           我是span
       </span>
    </div>
</body>
<script src="./MVVM/mvvm.js"></script>
<script src="./MVVM/observer.js"></script>
<script src="./MVVM/compile.js"></script>
<script src="./MVVM/watcher.js"></script>
<script>
    var vm = new MVVM({
        el:"#app",
        data: {
           msg:"big"
        }
    })

    setTimeout(()=>{
        vm.msg = "small"
    },2000)
</script>
</html>